The present invention relates generally to aircraft refueling booms and more specifically to a system and method to provide boom load alleviation.
Aircraft in flight are commonly refueled from a refueling aircraft. The refueling aircraft is typically provided with a boom mechanism or a flexible hose which trails behind the aircraft and physically makes a connection to the aircraft to be refueled. Many refueling aircraft use a system of fixed and extendable metal tubing to provide the fluid connection for refueling an aircraft. For the tube type system, a fixed tube is normally attached to the aircraft and a distal end of the fixed tube provides for an extendable length of tubing. An operator in the refueling aircraft either visually or with the assistance of camera equipment can visually observe the extension of the tubing to align the tubing to the receiving aircraft.
The tube type refueling boom normally has steerable fins or ailerons attached at specific locations to allow the refueling operator to xe2x80x9cflyxe2x80x9d the refueling boom. Hydraulic controls allow the boom operator to therefore steer the boom towards the aircraft to be refueled.
Once the refueling boom is connected to the aircraft to be fueled, most tube type refueling booms in use do not provide for automatic boom load alleviation. Stresses are placed on a boom due to the motion of the refueling aircraft, as well as from the aircraft to be refueled. These stresses can result in boom failure. In these systems, the boom operator is responsible to continue to steer the boom during the refueling operation whenever the boom appears to be deflecting. A typical boom extends out between approximately 12.2 meters (m) to 15.2 m (40-50 feet) in its fully extended position. It is therefore difficult for the boom operator to visually detect a deflection at the end of the boom adjacent to the aircraft to be fueled. A drawback of manually steering the boom is that boom stresses can build up before the operator is aware of the boom deflection.
A boom load alleviation system employing strain gauges to identify the load on a boom in use is known. This load alleviation system relies on electrical feedback from the strain gauges to a computer onboard the aircraft which identifies a boom bending load. The strain gage signals are analyzed by the computer which provides automatic control to re-steer the boom back to a lower load position. The disadvantage of this strain gauge type load alleviation system is the expense of the equipment, the maintenance of the strain gauge equipment, and the potential for damage to the strain gages since the refueling boom adjacent to the strain gauge installation commonly contacts the aircraft to be refueled.
A need therefore exists for a simplified boom load alleviation system which provides a simpler, less expensive, and more durable system.
According to a preferred embodiment of the present invention, a boom load alleviation system and method for refueling an aircraft uses a passive visual system to identify refueling boom deflection. The system of the present invention provides at least one digital camera mounted from the section of the aircraft adjacent to a refueling boom fixed attachment point. At least one set of targeting sights is attached to a fixed boom at its distal end in visual alignment with at least one of the digital cameras. At least one set of targeting sights, which are in visual alignment with the same digital camera are attached adjacent to a boom nozzle at the distal end of an extendable boom. The digital cameras each receive pixel images of the targeting sights and the pixel images are relayed to an onboard computer. The computer is previously provided with data tables identifying the length of both the fixed boom and the extendable boom.
When the boom nozzle connects with the aircraft to be refueled, a boom null position is programmed. The null position is the extended but non-deflected position of the refueling boom. The boom load alleviation system thereafter signals for a boom position change when either or both of two boom deflection conditions are present. In one condition, when the pixel images of the targeting sights at the extendable end of the boom change position from the null position, an X or Y coordinate change of the extendable boom targeting sights indicates a boom deflection. In a second condition, when the quantity of pixels identifying an extendable boom targeting sight changes, indicating a targeting sight motion toward or away from the digital camera, a boom deflection is also indicated.
When a displacement between the sets of targeting sights is indicated, the direction and degree of displacement of the extended boom is determined and the computer provides the necessary instructions to the boom operator and/or to an existing (or retrofitted) automatic control system to steer the refueling boom back to its null position. The boom load alleviation system of the present invention is switched between either an On or an Off position. In the On position, the refueling boom is automatically steered to return it to its null position. In the Off position, the boom load alleviation system of the present invention provides an indication to the boom operator of the relative displacement of the boom sections, but the boom operator must manually relocate or xe2x80x9cflyxe2x80x9d the refueling boom to its null position.
The boom load alleviation system of the present invention also communicates with other sensing systems of the aircraft, including the existing boom elevation, azimuth, and nozzle extension length information sensors. The boom load alleviation system of the present invention is normally in continuous operation to continuously analyze targeting sight data indicating a deflection between the boom fixed tube and the boom extended tube. Continuous feedback to the boom operator and to the boom automatic control system is therefore provided.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.